Abstract

Experiments designed to demonstrate the action of natural selection on a polymorphic locus can provide convincing results only if they relate to a polymorphism whose genetic and ecological environment reflects that found in nature. Two important practical problems arise from this. First, laboratory experiments using only a small sample of alleles from a natural population may produce a misleading appearance of selection on the locus under investigation as a result of sampling disequilibria between this locus and others which are more responsive to selection. This effect can be avoided by using adequate samples from nature (Jones and Yamazaki 1974; Powell 1973). Secondly, investigations of polymorphism in, for example, a Drosophilapopulation cage are open to the criticism that the laboratory environment lacks important components of selection which may be present in nature. A failure to demonstrate selection in such conditions may therefore not be a real indication of selective neutrality. Thus, attempts to simulate the natural environment (such as adding ethanol to the medium when studying the alcohol dehydrogenase polymorphism? see Clarke, this symposium) sometimes reveal previously undetected selective differences. Experiments on populations in their natural environment avoids this problem.

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